The complex cell wall of these gram-positive actinomycetes is their most characteristic feature and its biosynthesis is the target of some of the most effective antimycobacterial agents. Historically, this project has focussed on understanding the biosynthesis of various cell wall constituents through the use of the classical techniques of protein purification and analysis as well as genetic manipulation of various mycobacterial species. Currently this project focusses on the chemical synthesis of derivatives of a natural product that targets an enzyme involved in the biosynthesis of the mycobacterial cell wall. Mycolic acids are complex alpha-branched, beta-hydroxy fatty acids that are unique to mycobacteria which are heavily modified by a variety of functional groups. Mycolic acids are biosynthetically produced through an extension of normal fatty acid metabolism. In mycobacteria this is initiated by a "eukaryotic"-like Type I fatty acid synthase, a large multifunctional enzyme that produces primarily short-chain (16-24 carbons) fatty acids that are then substrates for a second fatty acid synthase system that is more typically associated with bacteria. This Type II system appears to be the molecular target for isoniazid as well as other inhibitors such as triclosan. Thiolactomycin is a low molecular weight natural product isolated from a soil Nocardia species that specifically inhibits one component of the bacterial Type II fatty acid synthase system. Although it is a modest inhibitor against most bacteria it has shown in vivo activity in various experimental infections of animals. Our collaborators at St Jude's Children's Hospital in Memphis have solved the crystal structure of thiolactomycin in complex with its target, the beta-ketoacyl ACP synthase, from E coli. In collaboration with GlaxoSmithKline we are currently synthesizing and testing derivatives of thiolactomycin to produce analogs with improved potency against tuberculosis. Using the co-crystal of thiolactomycin with its target as a guide, we are attempting to make rational improvements in the structure which should improve binding to the active site of this enzyme.